Abnormality detection apparatus for electrically heated catalyst

ABSTRACT

An abnormality detection apparatus calculates an actually supplied electrical energy defined as the integrated value of electrical power actually supplied to the electrically heated catalyst over a specific period from the time when the supply of electrical power to the electrically heated catalyst is started and a target electrical energy in the specific period, and further calculates, from these integrated values, an accomplishment parameter relating to the ratio of the actually supplied electrical energy to the target electrical energy. The abnormality detection apparatus detects an abnormality of the electrically heated catalyst by comparing the accomplishment parameter with a specific threshold. The abnormality detection apparatus is configured to set the specific threshold according to the temperature of the electrically heated catalyst at the time when the supply of electrical power is started.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2019-006357, filed on Jan. 17, 2019, which is hereby incorporated by reference herein in its entirety.

BACKGROUND Technical Field

The present disclosure relates to an abnormality detection apparatus for an electrically heated catalyst.

Description of the Related Art

There are known exhaust gas purification apparatuses for internal combustion engines that include an exhaust gas purification catalyst adapted to be heated by a heating element that is energized electrically. Such a catalyst will also be referred to as “electrically heated catalyst” hereinafter. The electrically heated catalyst of such an exhaust gas purification apparatus for an internal combustion engine is energized (or supplied with electrical power) before the startup of the internal combustion engine to reduce exhaust emissions during and/or just after the startup of the internal combustion engine.

If the electrically heated catalyst has an abnormality or problem, there may be cases where it is not heated to an intended temperature even if a normal amount of electrical energy is supplied to it. It is known to detect an abnormality of an electrically heated catalyst by comparing the integrated value of electrical power actually supplied to the electrically heated catalyst (which will be also referred to as “actual electrical power” hereinafter) and the integrated value of a standard electrical power (see, for example, Patent Literature 1 in the citation list below).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open No. 2000-220443

SUMMARY

In cases where the base material of the heating element of the electrically heated catalyst is a material whose electrical resistance decreases with rise of temperature (namely, a material having NTC characteristics), such as SiC, there is a possibility that the accuracy of abnormality detection may be deteriorated due to influence of the temperature of the heating element on the actual electrical power. In particular, at low temperatures, where the electrical resistance of the heating element is large, the actual electrical power can be lower than a standard electrical power, even if the highest possible voltage is applied to the electrically heated catalyst. Then, even if the electrically heated catalyst is normal, the difference between the actual electrical power and the standard electrical power may become large. This may make it difficult to detect an abnormality of the electrically heated catalyst with high accuracy. The difference between the actual electrical power and the standard electrical power varies depending on the temperature of the electrically heated catalyst at the time when the supply of electrical power is started. This makes it difficult to detect an abnormality of the electrically heated catalyst with high accuracy using a constant criterion.

The present disclosure has been made in the above circumstances, and an object of the present disclosure is to provide a technology that enables accurate detection of abnormalities of electrically heated catalysts provided with a heating element having NTC characteristics irrespective of its temperature at the time when supply of electrical power to it is started.

According to the present disclosure, there is provided an abnormality detection apparatus for an electrically heated catalyst that detects an abnormality of an electrically heated catalyst by comparing the ratio of the electrical energy actually supplied to the electrically heated catalyst over a specific period from the time when the supply of electrical power is started with a specific threshold. The abnormality detection apparatus is configured to vary the specific threshold according to the temperature of the electrically heated catalyst at the time when the supply of electrical power to the electrically heated catalyst is started.

Specifically, an abnormality detection apparatus for an electrically heated catalyst according to the present disclosure comprises: an electrically heated catalyst provided in an exhaust passage of an internal combustion engine, including an exhaust gas purification catalyst and a heating element that generates heat when supplied with electrical power, the electrical resistance of the heating element being larger when its temperature is low than when it is high; and a controller including at least one processor.

The controller is configured to:

adjust an applied voltage defined as a voltage applied to the electrically heated catalyst in such a way as to make the electrical power as the product of the applied voltage and a catalyst current defined as the electrical current flowing through the electrically heated catalyst per unit time equal to a target electrical power to be supplied to the electrically heated catalyst, and adjust the applied voltage to a voltage substantially equal to a specific upper limit voltage when the electrical power that can be supplied to the electrically heated catalyst by applying a voltage equal to or lower than the specific upper limit voltage is lower than the target electrical power;

calculate an actually supplied electrical energy defined as the integrated value of the electrical power actually supplied to the electrically heated catalyst over a specific period from the time when the application of the applied voltage to the electrically heated catalyst by the controller is started;

calculate a target electrical energy defined as the integrated value of the target electrical power over the specific period;

calculate an accomplishment ratio parameter relating to the ratio of the actually supplied electrical energy calculated by the controller to the target electrical energy calculated by the controller; and

detect an abnormality of the electrically heated catalyst by comparing the accomplishment ratio parameter calculated by the controller and a specific threshold.

The controller is further configured to:

acquire a temperature parameter relating to the temperature of the electrically heated catalyst at the time when the supply of electrical power is started; and

set the specific threshold according to the temperature parameter acquired by the controller.

In cases where the electrically heated catalyst is provided in a vehicle, when the temperature of the electrically heated catalyst (or exhaust gas purification catalyst) is low, as is the case when the internal combustion engine is cold-started, the controller applies a voltage (or supplies electrical power) to the electrically heated catalyst before the startup of the internal combustion engine to cause the heating element to generate heat, thereby preheating the exhaust gas purification catalyst. In this process, the controller controls the voltage applied to the electrically heated catalyst (applied voltage) in such a way as to make the electrical power as the product of the applied voltage and the current flowing through the electrically heated catalyst per unit time (catalyst current) equal to a target electrical power to be supplied to the electrically heated catalyst (namely, a target value of the electrical power to be supplied to the electrically heated catalyst). This can enhance the cleaning performance of the electrically heated catalyst in the period during and just after the startup of the internal combustion engine, leading to a reduction of exhaust emissions. The target electrical power mentioned above is set taking account of factors such as the structure and performance of a device(s) used to supply electrical power to the electrically heated catalyst (e.g. a battery, a generator, and/or a DC-to-DC converter).

If an abnormality such as oxidation of the heating element or electrodes or a crack thereof occurs in the electrically heated catalyst, there is a possibility that the electrical resistance of the electrically heated catalyst may become larger than that in the normal condition. When this occurs, even if the applied voltage is set to the highest voltage (or the specific upper limit mentioned above) that can be applied to the electrically heated catalyst, there is a possibility that the electrical power that can be supplied to the electrically heated catalyst may be smaller than the target electrical power due to insufficiency in the catalyst current. This can make it difficult to preheat the electrically heated catalyst effectively in a limited time before the startup of the internal combustion engine. To avoid such a situation from occurring, it is necessary to detect abnormalities like those described above with high accuracy.

In the case where the electrically heated catalyst (or its heating element) has NTC characteristics, the electrical resistance of the electrically heated catalyst is larger when its temperature is low than when it is high. In consequence, when the temperature of the electrically heated catalyst is relatively low, as is the case just after the start of the supply of electrical power to the electrically heated catalyst, the electrical resistance of the electrically heated catalyst can be relatively large, even if the electrically heated catalyst is normal. The voltage that can be applied to the electrically heated catalyst has a specific upper limit that is determined by the structure and performance of the device(s) used to supply electrical power to the electrically heated catalyst. Therefore, if the applied voltage is limited to this upper limit when the electrical resistance of the electrically heated catalyst is large due to its relatively low temperature, as is generally the case just after the start of power supply to the electrically heated catalyst, the catalyst current can be insufficient, even if the electrically heated catalyst is in a normal condition. Then, the electrical power actually supplied to the electrically heated catalyst (actual electrical power) can be lower than the target electrical power, even if the electrically heated catalyst is normal.

The abnormality detection apparatus for an electrically heated catalyst according to the present disclosure is configured to calculate the integrated value of electrical power actually supplied to the electrically heated catalyst over a specific period from the time when the application of the applied voltage to the electrically heated catalyst by the controller is started (actually supplied electrical energy) and the integrated value of the target electrical power over the specific period (target electrical energy) and to calculate, from these integrated values, a parameter (accomplishment ratio parameter) relating to the ratio of the actually supplied electrical energy to the target electrical energy. Moreover, the abnormality detection apparatus for an electrically heated catalyst according to the present disclosure is configured to detect abnormality of the electrically heated catalyst by comparing the accomplishment ratio parameter with a specific threshold. The aforementioned specific period is set as such a period during which there will be a significant difference between the accomplishment parameter in the case where the electrically heated catalyst is normal and that in the case where the electrically heated catalyst is abnormal. For example, the specific period as such may be set as a period longer than the time needed for the actual electrical power to substantially reach the target electrical power after the start of the supply of electrical power to the electrically heated catalyst and shorter than the time needed for the target electrical energy to reach a standard amount of electrical energy after the start of the supply of electrical power to the electrically heated catalyst when the electrically heated catalyst is normal. The standard amount of electrical energy mentioned above is, for example, an amount of electrical energy that is needed to raise the temperature of the electrically heated catalyst from its initial temperature at the time when the supply of electrical power is started to a specific temperature (e.g. a temperature at which the exhaust gas purification catalyst becomes active).

In the case where the electrically heated catalyst has NTC characteristics, the electrical resistance of the electrically heated catalyst during the supply of electrical power thereto varies depending on the temperature of the electrically heated catalyst at the time when the supply of electrical power is started. In consequence, the ratio of the actually supplied electrical energy to the target electrical energy may also vary accordingly. For example, the electrical resistance of the electrically heated catalyst during the supply of electrical energy thereto is smaller when the temperature of the electrically heated catalyst at the time of the start of power supply is high than when it is low, and accordingly, the ratio of the actually supplied electrical energy to the target electrical energy is higher when the temperature of the electrically heated catalyst at the time of the start of power supply is high than when it is low. For this reason, if the specific threshold is set as a constant value without regard to the temperature of the electrically heated catalyst at the time when the supply of electrical power is started, it may be difficult to detect an abnormality of the electrically heated catalyst with high accuracy.

In view of the above, the abnormality detection apparatus for an electrically heated catalyst according to the present disclosure is configured to acquire a temperature parameter relating to the temperature of the electrically heated catalyst at the time when the supply of electrical power is started and to set the specific threshold based on the temperature parameter. The temperature parameter may simply be the temperature of electrically heated catalyst at the time when the supply of electrical power is started. Alternatively, the temperature parameter may be the temperature of the electrically heated catalyst at the time during the specific period at which the actually supplied electrical energy since the start of the supply of electrical power reaches a predetermined amount of electrical energy. The temperature of the electrically heated catalyst at that time during the specific period may be calculated, for example, by adding the amount of rise in the temperature of the electrically heated catalyst resulting from the supply of the predetermined amount of electrical energy to the temperature of the electrically heated catalyst at the time when the supply of electrical power is started.

Configured as above, the abnormality detection apparatus for an electrically heated catalyst according to the present disclosure detects an abnormality of the electrically heated catalyst based on the specific threshold that is set according to the temperature of the electrically heated catalyst at the time when the supply of electrically power thereto is started. Therefore, the abnormality detection apparatus for an electrically heated catalyst according to the present disclosure can detect abnormalities of the electrically heated catalyst having NTC characteristics with high accuracy irrespective of the temperature of the electrically heated catalyst at the time when the supply of electrical power to it is started.

The controller according to the present disclosure may be configured to calculate a supplied electrical energy ratio defined as the ratio of the actually supplied electrical energy to the target electrical energy as the accomplishment ratio parameter. In this case, the controller may determine that the electrically heated catalyst is abnormal if the supplied electrical energy ratio calculated by the controller is lower than a specific ratio as the specific threshold. The controller may set the specific ratio larger when the temperature parameter acquired by the controller is large than when it is small.

As described above, the electrical resistance of the electrically heated catalyst is larger when the electrically heated catalyst is abnormal than when it is normal. In consequence, the supplied electrical energy ratio is smaller when the electrically heated catalyst is abnormal than when it is normal. In the case of the electrically heated catalyst having NTC characteristics, the electrical resistance during the supply of electrical power to it is smaller when the temperature of the electrically heated catalyst at the time of start of power supply is high than when it is low. In consequence, the difference between the actually supplied electrical energy and the target electrical energy is smaller, and accordingly, the supplied electrical energy ratio is higher when the temperature of the electrically heated catalyst at the time of start of power supply is high than when it is low. Therefore, the value of the aforementioned specific ratio is set larger when the temperature parameter is large (or when the temperature of the electrically heated catalyst at the time of start of power supply is high) than when the temperature parameter is small (or when the temperature of the electrically heated catalyst at the time of start of power supply is low). This enables the abnormality detection apparatus to detect abnormalities of the electrically heated catalyst with high accuracy irrespective of the temperature of the electrically heated catalyst at the time when the supply of electrical power to it is started.

The accomplishment ratio parameter according to the present disclosure is not limited to the supplied electrical energy ratio. For example, a supplied electrical energy difference defined as the difference between the actually supplied electrical energy calculated by the controller and the target electrical energy calculated by the controller may serve as the accomplishment ratio parameter. In the case of the electrically heated catalyst having NTC characteristics, the electrical resistance during the supply of electrical power to it is smaller when the temperature of the electrically heated catalyst at the time of start of power supply is high than when it is low, and accordingly, the supplied electrical energy difference is smaller when the temperature of the electrically heated catalyst at the time of start of power supply is high than when it is low. Therefore, in the case where the supplied electrical energy difference is used as the accomplishment ratio parameter, the value of the specific threshold is to be set smaller when the temperature of the electrically heated catalyst at the time of start of power supply is high than when it is low.

The present disclosure enables an abnormality detection apparatus to accurately detect an abnormality of an electrically heated catalyst provided with a heating element having NTC characteristics irrespective of its temperature at the time when supply of electrical power to it is started.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the general configuration of a vehicle to which the present disclosure is applied.

FIG. 2 is a diagram illustrating the general configuration of an electrically heated catalyst (EHC).

FIG. 3 is a graph illustrating relationship between the soak time and the bed temperature Tcat.

FIG. 4 illustrates changes of the actual electrical power Wr, the actually supplied electrical energy ΣWr, and the bed temperature Tcat of a catalyst carrier with time during a period from the start to the end of supply of electrical power to the EHC.

FIG. 5 is a graph illustrating relationship between the bed temperature Tcat of the catalyst carrier and the electrical resistance Rcat of the EHC.

FIG. 6 illustrates changes of the actual electrical power Wr, and the actually supplied electrical energy ΣWr with time in a case where preheating is performed when the EHC has an abnormality.

FIG. 7 is a graph illustrating how the initial bed temperature T0 affects the actual electrical power Wr.

FIG. 8 is a graph illustrating relationship between the initial bed temperature T0 and the supplied electrical energy ratio Prw at the time when a specific period has elapsed since the start of power supply to the EHC.

FIG. 9 is a flow chart of a processing routine executed by an ECU in an abnormality detection process according to an embodiment.

DESCRIPTION OF EMBODIMENTS

In the following, a specific embodiment of the present disclosure will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and other features of the components that will be described in connection with the embodiments are not intended to limit the technical scope of the present disclosure only to them, unless otherwise stated.

Embodiment

FIG. 1 is a diagram illustrating the general configuration of a vehicle to which the present disclosure is applied. The vehicle 100 illustrated in FIG. 1 is provided with a hybrid system that drives wheels (driving wheels) 58. The hybrid system includes an internal combustion engine 1, a power split device 51, an electric motor 52, a generator 53, a battery 54, a power control unit (PCU) 55, an axle (or drive shaft) 56, and a reduction gear 57.

The internal combustion engine 1 is a spark-ignition internal combustion engine (or gasoline engine) having a plurality of cylinders 1 a. The internal combustion engine 1 has ignition plugs 1 b, each of which ignites air-fuel mixture formed in each cylinder 1 a. While the internal combustion engine 1 illustrated in FIG. 1 has four cylinders, the present disclosure may be applied to internal combustion engines having less or more than four cylinders. Alternatively, the internal combustion engine 1 may be a compression-ignition internal combustion engine (or diesel engine). The output shaft (crankshaft) of the internal combustion engine 1 is connected to the rotary shaft of the generator 53 and the rotary shaft of the electric motor 52 through the power split device 51.

The rotary shaft of the generator 53 is connected to the crankshaft of the internal combustion engine 1 through the power split device 51 and generates electrical power mainly using the kinetic energy of the crankshaft. The electric motor 53 can also function as a starter motor by rotating the crankshaft through the power split device 51 when starting the internal combustion engine 1. The electrical power generated by the generator 53 is supplied to the electric motor 52 or stored in the battery 54 by the PCU 55.

The rotary shaft of the electric motor 52 is connected to the axle 56 through the reduction gear 57 and capable of rotating the wheels 58 using the electrical power supplied from the battery 54 or the generator 53 through the PCU 55. The rotary shaft of the electric motor 52 is connected to the power split device 51 also, and the electric motor 52 is capable of assisting the internal combustion engine 1 in rotating the wheels 58.

The power split device 51 includes a planetary gear device. The power split device 51 splits power among the internal combustion engine 1, the electric motor 52, and the generator 53. For example, the power split device 51 control the travelling speed of the vehicle 100 by causing the electric motor 52 to operate with controlled power generated by the generator 53 while causing the internal combustion engine 1 to operate in the most efficient operation range.

The PCU 55 includes an inverter, a step-up converter, and a DC-to-DC converter. The PCU 55 converts direct current power supplied from the battery 54 into alternating current power to supply it to the electric motor 52, converts the alternating current power supplied from the generator 53 into direct current power to supply it to the battery 54, transforms the voltage of power between the inverter and the battery 54, and transforms the voltage of power supplied from the battery 54 to an electrically heated catalyst (EHC) 2, which will be described later.

The internal combustion engine 1 has fuel injection valves each of which injects fuel into each cylinder 1 a or intake port. Air-fuel mixture formed by air and fuel injected through the fuel injection valve is ignited by the ignition plug 1 b and burns to generate thermal energy, which is used to rotate the crankshaft.

The internal combustion engine 1 is connected with an intake pipe 10. The intake pipe 10 delivers fresh air taken in from the atmosphere to the cylinders of the internal combustion engine 1. The intake pipe 10 is provided with an air flow meter 12 and a throttle valve 13. The air flow meter 12 outputs an electrical signal relating to the mass of the air supplied to the internal combustion engine 1 (or intake air quantity). The throttle valve 13 varies the channel cross sectional area in the intake pipe 10 to control the intake air quantity of the internal combustion engine 1.

The internal combustion engine 1 is also connected with an exhaust pipe 11, through which burned gas (or exhaust gas) burned in the cylinders of the internal combustion engine 1 flows. The exhaust pipe 11 is provided with an EHC 2 as an exhaust gas purification catalyst. The EHC 2 is provided with a heater that generates heat by electrical current supplied to it. The exhaust pipe 11 is provided with an air-fuel ratio sensor (A/F sensor) 14 and a first exhaust gas temperature sensor 15, which are arranged upstream of the EHC 2. The A/F sensor 14 outputs an electrical signal relating to the air-fuel ratio of the exhaust gas. The first exhaust gas temperature sensor 15 outputs an electrical signal relating to the temperature of the exhaust gas flowing into the EHC 2. The exhaust pipe 11 is also provided with a second exhaust gas temperature sensor 16, which is arranged downstream of the EHC 2. The second exhaust gas temperature sensor 16 outputs an electrical signal relating to the temperature of the exhaust gas flowing out of the ECH 2. Alternatively, the exhaust pipe 11 may be provided with only one of the first and second exhaust gas temperature sensors 15, 16, in other words one of the first and second exhaust gas temperature sensors 15, 16 may be eliminated.

An electronic control unit (ECU) 20 is provided for the above-described hybrid system. The ECU 20 is an electronic control unit including a CPU, a ROM, a RAM, and a backup RAM.

The ECU 20 is electrically connected with the air flow meter 12, the A/F sensor 14, the first exhaust gas temperature sensor 15, the second exhaust gas temperature sensor 16, and an accelerator position sensor 17. The accelerator position sensor 17 outputs an electrical signal relating to the amount of depression of the accelerator pedal (or accelerator opening degree).

The ECU 20 controls the internal combustion engine 1 and its peripheral devices (such as the ignition plugs 1 b, the throttle valve 13, and the fuel injection valves), the electric motor 52, the generator 53, the PCU 55, and the EHC 2 based on the signals output from the aforementioned sensors. The ECU 20 may be divided into an ECU that controls the hybrid system overall and an ECU that controls the internal combustion engine 1 and its peripheral devices.

The general configuration of the EHC 2 will now be described with reference to FIG. 2. The arrow in FIG. 2 indicates the direction of flow of exhaust gas. The EHC 2 includes a catalyst carrier 3 having a cylindrical shape, an inner cylinder 6 having a cylindrical shape that covers the catalysts carrier 3, and a cylindrical case 4 that covers the inner cylinder 6. The catalyst carrier 3, the inner cylinder 6, and the case 4 are arranged coaxially.

The catalyst carrier 3 is a structure having a plurality of passages extending along the direction of exhaust gas flow and arranged in a honeycomb pattern. The catalyst carrier 3 has a cylindrical outer shape. The catalyst carrier 3 carries an exhaust gas purification catalyst 31. The exhaust gas purification catalyst 31 may be an oxidation catalyst, a three-way catalyst, an NOx storage reduction (NSR) catalyst, a selective catalytic reduction (SCR) catalyst, or a combination of such catalysts. The base material of the catalyst carrier 3 is a material having a relatively high electrical resistance that increases with rise of its temperature (namely, a material having NTC characteristics) and functions as a heating element. An example of such a material is a porous ceramic (e.g. SiC).

The inner cylinder 6 is an insulator with low conductivity and high heat resistance (e.g. alumina or stainless steel coated with an insulation layer on its surface) that is shaped as a cylinder. The inner cylinder 6 is dimensioned to have an inner diameter larger than the outer diameter of the catalyst carrier 3.

The case 4 is a housing made of a metal (e.g. stainless steel) that houses the catalyst carrier 3 and the inner cylinder 6. The case 4 has a cylindrical portion having an inner diameter larger than the outer diameter of the inner cylinder 6, an upstream conical portion joining to the upstream end of the cylindrical portion, and a downstream conical portion joining to the downstream end of the cylindrical portion. The upstream conical portion and the downstream conical portion are tapered in such a way that their inner diameters decrease as they extend away from the cylindrical portion.

A cylindrical mat member 5 is press-fitted in the gap between the inner circumference of the inner cylinder 6 and the outer circumference of the catalyst carrier 3, and another mat member 5 is press-fitted in the gap between the inner circumference of the case 4 and the outer circumference of the inner cylinder 6. The mat member 5 is made of a low-conductive insulating material that provides high cushioning (e.g. an inorganic fiber mat, such as an alumina fiber mat).

The EHC 2 has two through-holes 9 that pass through the case 4, the mat members 5, and the inner cylinder 6. The through holes 9 are located at opposed positions on the outer circumference of the case 4. Electrodes 7 are provided in the respective through-holes 9. Each electrode 7 includes a surface electrode 7 a that extends circumferentially and axially along the outer circumference of the catalyst carrier 3 and a stem electrode 7 b that extends from the outer circumference of the surface electrode 7 a to the outside of the case 4 through the through-hole 9.

A support member 8 is provided between the case 4 and the stem electrode 7 b in the through-hole 9 to support the stem electrode 7 b. The support member 8 is adapted to stop the annular gap between the case 4 and the stem electrode 7 b. The support member 8 is made of an insulating material with low conductivity to prevent short-circuit between the stem shaft 7 b and the case 4.

The stem electrodes 7 b are connected to the output terminals of the battery 54 through a power supply control unit 18 and the PCU 55. The power supply control unit 18 is a unit controlled by the ECU 20 and has the functions of applying a voltage to the electrodes 7 from the battery 54 through the PCU 55 (i.e. power supply to the EHC 2), controlling the voltage applied to the EHC 2 (or applied voltage) from the battery 54 through the PCU 55, and sensing the current flowing between the electrodes 7 of the EHC 2 per unit time (or catalyst current).

With the above configuration of the EHC 2, when the power supply control unit 18 applies a voltage from the battery 54 to the electrodes 7 through the PCU 55 to energize (in other words, supply electrical power to) the EHC 2, the catalyst carrier 3 behaves as a resistor to generate heat. In consequence, the exhaust gas purification catalyst 31 carried by the catalyst carrier 3 is heated. Thus, if the EHC 2 is energized when the temperature of the exhaust gas purification catalyst 31 is low, it is possible to raise the temperature of the exhaust gas purification catalyst 31 promptly. In particular, energizing the EHC 2 before the startup of the internal combustion engine 1 can reduce exhaust emissions during and just after the startup of the internal combustion engine 1.

In the following, a method of controlling the EHC 2 according to the embodiment will be described. The power supply control unit 18 is controlled in such a way as to energize the EHC 2 if the internal combustion engine 1 is not operating and the temperature of the catalyst carrier 3 is lower than a specific temperature (e.g. a temperature at which the exhaust gas purification catalyst 31 carried by the catalyst carrier 3 is made active) while the hybrid system is in an activated state (that is, a state in which the system can drive the vehicle).

Specifically, when the hybrid system is activated, the ECU 20 firstly senses the state of charge (SOC) of the battery 54. The SOC is the ratio of the amount of electrical energy that the battery 54 can discharge at present to the maximum electrical energy that the battery 54 can store (namely, the electrical energy stored in the fully-charged battery). The SOC is calculated by integrating the current charged into and discharged from the battery 54.

The ECU 20 determines the temperature of the central portion of the catalyst carrier 3 at the time of activation of the hybrid system. This temperature will also be referred to as the “bed temperature” hereinafter. Specifically, the ECU 20 estimates the bed temperature at that time on the basis of the bed temperature Tend at the time when the operation of the internal combustion engine 1 was stopped last time and the time elapsed from the time when the operation of the internal combustion engine 1 was stopped last time to the time of activation of the hybrid system, namely the soak time.

FIG. 3 illustrates the relationship between the bed temperature Tcat of the catalyst carrier 3 and the soak time. After the operation of the internal combustion engine 1 is stopped (at t0 in FIG. 3), the catalyst temperature Tcat of the catalyst carrier 3 falls with time from the bed temperature Tend at the time when the operation of the internal combustion engine 1 is stopped last time. The bed temperature Tcat of the catalyst carrier 3 decreases to eventually become close to the ambient temperature Tatm (at t1 in FIG. 3), and thereafter the bed temperature Tcat is stable at a temperature equal to or close to the ambient temperature Tatm. The system according to the embodiment determines the relationship illustrated in FIG. 3 in advance by experiment or simulation and stores this relationship in the ROM or other component of the ECU 20 as a map or a function expression that enables determination of the bed temperature at the time of activation of the hybrid system from the bed temperature Tend at the time of stopping of the operation of the internal combustion engine 1 and the soak time as arguments. Alternatively, the bed temperature Tend at the time of stopping of the operation of the internal combustion engine 1 may be estimated from the measurement values of the first exhaust gas temperature sensor 15 and/or the second exhaust gas temperature sensor 16 immediately before the stopping of the operation of the internal combustion engine 1 or from the history of the previous operation of the internal combustion engine 1.

Then, the ECU 20 determines whether or not the bed temperature of the catalyst carrier 3 at the time of activation of the hybrid system is lower than a specific temperature. If the bed temperature of the catalyst carrier 3 at the time of activation of the hybrid system is lower than the specific temperature, the ECU 20 calculates the amount of electrical energy that is needed to be supplied to the EHC 2 to raise the bed temperature of the catalyst carrier 3 to the specific temperature. This electrical energy will be referred to as the “standard amount of electrical energy” hereinafter. The standard amount of electrical energy calculated is larger when the bed temperature of the catalyst carrier 3 at the time of activation of the hybrid system is low than when it is high. Then, the ECU 20 calculates a consumption SOCcom of the SOC that will result if the standard amount of electrical energy is supplied to the EHC 2. Then, the ECU 20 calculates the remaining amount ΔSOC of the SOC by subtracting the consumption SOCcom from the SOC at the time of activation of the hybrid system (ΔSOC=SOC−SOCcom). The ECU 20 determines whether or not the remaining amount ΔSOC thus calculated is larger than a lower limit. This lower limit is a value of SOC below which it is considered necessary to charge the battery 54 by starting the internal combustion engine 1.

If the remaining amount ΔSOC is larger than the lower limit, the ECU 20 starts the supply of electrical power to the EHC 2 at the time when the SOC becomes equal to the sum of the consumption SOCcom and the lower limit plus a margin. If the remaining amount ΔSOC is larger than an amount that enables the vehicle 100 to travel in the EV mode (the mode in which the vehicle 100 is driven by the electric motor 52 only) for a certain length of time, the vehicle 100 may be driven only by the electric motor 52 when a request for driving the vehicle 100 is made, and the supply of electrical power to the EHC 2 may be started. The aforementioned “certain length of time” is, for example, a length of time longer than the length of time required to supply the standard amount of electrical energy to the EHC 2.

When supplying electrical power to the EHC 2, the ECU 20 sets a target value of electrical power (target electrical power) to be supplied to the EHC 2. The target electrical power is a constant value that is set taking account of factors such as the structure and performance of the devices used to supply electrical power to the EHC 2 (e.g. the generator 53, the battery 54, and the PCU 55). The ECU 20 controls the power supply control unit 18 in such a way as to adjust the electrical power supplied to the EHC 2 to the target electrical power. The electrical power supplied to the EHC 2 is the product of the voltage applied to the electrodes 7 of the EHC 2 (which will be referred to as “applied voltage”) and the current flowing between the electrodes 7 of the EHC 2 per unit time (which will be referred to as the “catalyst current”).

FIG. 4 illustrates changes in the electrical power actually supplied to the EHC 2 (which will be referred to as “actual electrical power Wr” hereinafter), the integrated value of the actual electrical power (which will be referred to as “actually supplied electrical energy ΣWr”), and the bed temperature Tcat of the catalyst carrier 3 with time during the period from the start to the end of the supply of electrical power to the EHC 2.

As illustrated in FIG. 4, the actual electrical power Wr is lower than the target power Wtrg during the period from the start of the supply of electrical power to the EHC 2 (at t10 in FIG. 4) to time t20 in FIG. 4. This is because the catalyst carrier 3 of the EHC 2 has NTC characteristics and the voltage that can be applied to the EHC 2 is lower than a specific upper limit. Specifically, when the catalyst carrier 3 has NTC characteristics, the electrical resistance of the catalyst carrier 3 is larger when the bed temperature Tcat of the catalyst carrier 3 is low than when it is high, and accordingly the electrical resistance Rcat of the EHC 2 including the catalyst carrier 3 and the electrodes 7 (in other words, the electrical resistance between the electrodes 7) also is larger when the bed temperature Tcat of the catalyst carrier 3 is low than when it is high, as will be seen in FIG. 5. Therefore, when the bed temperature Tcat of the catalyst carrier 3 is relatively low, as is the case just after the start of the supply of electrical power to the EHC 2, the electrical resistance Rcat of the EHC 2 is relatively large. The voltage that can be applied to the EHC 2 has a design upper limit (specific upper limit voltage) that is determined by the structure and performance of the device used to supply electrical power to the EHC 2. Therefore, when the bed temperature Tcat of the catalyst carrier 3 is relatively low, as is the case just after the start of electrical power supply to the EHC 2, since the electrical resistance Rcat of the EHC 2 is relatively large because of its NTC characteristics, the catalyst current will be unduly small even if the voltage as high as the specific upper limit voltage is applied to the EHC 2, resulting in actual electrical power Wr lower than the target electrical power Wtrg.

As the voltage as high as the upper limit voltage continues to be applied to the EHC 2 during the period from t10 to t20 in FIG. 4, the bed temperature Tcat of the catalyst carrier 3 rises with time from the temperature T0 at the time of starting the supply of electrical power, and the electrical resistance Rcat of the EHC 2 decreases with time consequently. In consequence, the catalyst current increases with time, and the actual electrical power Wr also increases with time accordingly. Eventually at time t20 in FIG. 4, the electrical resistance Rcat of the EHC 2 becomes so small that the actual electrical power Wr under the application of the upper limit voltage to the EHC 2 becomes substantially equal to the target electrical power Wtrg. After time t20 in FIG. 4, it is possible to keep the actual electrical power Wr substantially equal to the target electrical power Wtrg by decreasing the voltage applied to the EHC 2 with rise in the bed temperature Tcat of the catalyst carrier 3, in other words with decrease in the electrical resistance Rcat of the EHC 2. Specifically, the power supply control unit 18 measures the catalyst current (i.e. the current flowing between the electrodes 7 of the EHC 2 per unit time) and adjusts the applied voltage (i.e. the voltage resulting from transformation by the PCU 55) in such a way as to make the product of the measured catalyst current and the applied voltage (which is the actual electrical power Wr) substantially equal to the target electrical power Wtrg. When the actually supplied electrical energy ΣWr reaches the standard amount of electrical energy ΣWbase eventually (at t40 in FIG. 4), the bed temperature Tcat of the catalyst carrier 3 reaches the specific temperature Ttrg. Then, the ECU 20 controls the power supply control unit 18 to stop the supply of electrical power to the EHC 2.

As above, if the standard amount of electrical energy ΣWbase is supplied to the EHC 2 before the startup of the internal combustion engine 1, the catalyst carrier 3 and the exhaust gas purification catalyst 31 carried by the catalyst carrier 3 are heated to or above the specific temperature Ttrg. In consequence, the purification performance of the exhaust gas purification catalyst 31 in the period during and just after the startup of the internal combustion engine 1 is enhanced, leading to reduced exhaust emissions. In the following, the above-described process of preheating the exhaust gas purification catalyst 31 before the startup of the internal combustion engine 1 will be referred to as the “preheat process”.

If an abnormality such as oxidation of the catalyst carrier 3 or the electrodes 7 or a crack thereof occurs in the EHC 2, there is a possibility that the electrical resistance Rcat of the EHC 2 may become larger than that of the EHC 2 in the normal condition. When this is the case, the actual electrical power Wr becomes lower than that in the normal condition, and consequently the time (or power supply time) required to supply the standard amount of electrical energy ΣWbase to the EHC 2 may increase unduly. This may lead to difficulties in raising the bed temperature Tcat of the catalyst carrier 3 to the specific temperature Ttrg in a limited time before the startup of the internal combustion engine 1.

FIG. 6 illustrates changes in the actual electrical power Wr, the actually supplied electrical energy ΣWr, and the ratio Prw of the actually supplied electrical energy ΣWr to a target electrical energy Wtrg with time in a case where the preheat process is performed while an abnormality like those mentioned above is occurring in the EHC 2. The aforementioned ratio Prw will be hereinafter referred to as the “supplied electrical energy ratio”. In FIG. 6, the solid curves represent changes in the actual electrical power Wr1, the actually supplied electrical energy ΣWr1, and the supplied electrical energy ratio Prw1 in a case where the EHC 2 has an abnormality. The dot-dot-dash curves in FIG. 6 represent changes in the actual electrical power Wr0, the actually supplied electrical energy ΣWr0, and the supplied electrical energy ratio Prw0 with time in a case where the EHC 2 is normal. The dot-dash curves in FIG. 6 represent changes in the target electrical power Wtrg and the target electrical energy Wtrg with time.

In FIG. 6, during the period from the start of power supply to the EHC 2 (at t10 in FIG. 6) to the time when the actual electrical power Wr0 with the EHC 2 in the normal condition substantially reaches the target electrical power Wtrg (t20 in FIG. 6), the actual electrical power Wr0 with the EHC 2 in the normal condition and the actual electrical power Wr1 with the EHC 2 in the abnormal condition both differ from the target electrical power Wtrg due to NTC characteristics of the catalyst cattier 3, though the actual electrical power Wr0 with the EHC 20 in the normal condition is higher than the actual electrical power Wr1 with the EHC 2 in the abnormal condition. In consequence, the actually supplied electrical energy ΣWr0 with the EHC 2 in the normal condition and the actually supplied electrical energy ΣWr1 with the EHC 2 in the abnormal condition both differ from the target electrical energy ΣWtrg. Consequently, during the period from time t10 to time t20 in FIG. 6, the difference between the supplied electrical energy ratio Prw0 with the EHC 2 in the normal condition and the supplied electrical energy ratio Pwr1 with the EHC 2 in the abnormal condition is not large.

After time t20 in FIG. 6, the actual electrical power Wr0 with the EHC 2 in the normal condition is substantially equal to the target electrical power Wtrg, making the rate of increase of the bed temperature Tcat with the EHC 2 in the normal condition higher than that in the period before time t20 in FIG. 6. In consequence, the rate of increase of the actually supplied electrical energy ΣWr0 with the EHC 2 in the normal condition is larger than that in the period before time t20 in FIG. 6. On the other hand, since the actual electrical power Wr1 with the EHC 2 in the abnormal condition differs from the target electrical power Wtrg even after time t20 in FIG. 6, the rate of increase of the bed temperature Tcat with the EHC 2 in the abnormal condition does not significantly differ from that in the period before time t20 in FIG. 6, and accordingly the rate of increase of the actually supplied electrical energy ΣWr1 with the EHC 2 in the abnormal condition does not significantly differ from that in the period before time t20 in FIG. 6. In consequence, after time t20 in FIG. 6, the difference between the actually supplied electrical energy ΣWr0 with the EHC 2 in the normal condition and the actually supplied electrical energy ΣWr1 with the EHC 2 in the abnormal condition increases with time. Accordingly, the difference between the supplied electrical energy ratio Prw0 with the EHC 2 in the normal condition and the supplied electrical energy ratio Pwr1 with the EHC 2 in the abnormal condition increases with time after time t20 in FIG. 6. At the time when the target electrical energy ΣWtrg reaches the standard amount of electrical energy ΣWbase (t30 in FIG. 6), the actually supplied electrical energy ΣWr1 with the EHC 2 in the abnormal condition is significantly smaller than the actually supplied electrical energy ΣWr0 with the EHC 2 in the normal condition. In consequence, the supplied electrical energy ratio Pwr1 with the EHC 2 in the abnormal condition is significantly lower than the supplied electrical energy ratio Pwr0 with the EHC 2 in the normal condition at the time when the target electrical energy ΣWtrg reaches the standard amount of electrical energy ΣWbase (t30 in FIG. 6).

In this embodiment, detection of an abnormality of the EHC 2 is performed based on the supplied electrical energy ratio Prw at the time when the target electrical energy ΣWtrg reaches the standard amount of electrical energy ΣWbase (t30 in FIG. 6), in other words, based on the value of the supplied electrical energy ratio Prw upon the elapse of a specific period of time from the start of the supply of electrical power to the EHC 2. Specifically, if the value of the supplied electrical energy ratio Prw upon the elapse of the specific period of time from the start of the supply of electrical power to the EHC 2 is smaller than a specific ratio Pthre, it is determined that the EHC 2 is abnormal. The specific ratio Pthre mentioned above is such a value that if the value of the supplied electrical energy ratio Prw upon the elapse of the specific period of time from the start of the supply of electrical power to the EHC 2 is lower than the specific ratio Pthre, it may be determined that the EHC 2 is abnormal. In other words, the specific ratio Pthre is such a ratio that if the value of the supplied electrical energy ratio Prw upon the elapse of the specific period of time from the start of the supply of electrical power to the EHC 2 is lower than the specific ratio Pthre, it is difficult to preheat the EHC 2 effectively in a limited time before the startup of the internal combustion engine 1. The specific ratio Pthre is a value equal to the supplied electrical energy ratio Prw with the EHC 2 in the normal condition plus a margin that is set taking account of aged deterioration and variations of the EHC 2.

The value of the supplied electrical energy ratio Prw upon the elapse of the specific period of time from the start of the supply of electrical power to the EHC 2 can vary depending on whether the EHC 2 is normal or abnormal and on the bed temperature of the catalyst carrier 3 at the time when the supply of electrical power is started. This temperature will be also referred to as the “initial bed temperature” hereinafter.

How the bed temperature of the EHC 2 at the time when the supply of electrical power is started (which will also be referred to as the initial bed temperature T0) affects the actual electrical power Wr will be described with reference to FIG. 7. In FIG. 7, the solid curves represent changes in the actual electrical power Wr11, Wr12 with time in a case where the EHC 2 is abnormal. The dot-dot-dash curves in FIG. 7 represent changes in the actual electrical power Wr01, Wr02 with time in a case where the EHC 2 is normal. The dot-dash curve in FIG. 7 represents the target electrical power Wtrg.

As illustrated in FIG. 7, when the ECH 2 is normal (dot-dot-dash curves in FIG. 7), the actual electrical power that can be supplied to the EHC 2 just after the start of power supply is higher when the initial bed temperature T0 is high (Wr02) than when the initial bed temperature T0 is low (Wr01). In consequence, in the case where the EHC 2 is normal, the difference between the actual electrical power Wr02 for the higher initial bed temperature T0 and the target electrical power Wtrg is smaller than the difference between the actual electrical power Wr01 for the lower initial bed temperature T0 and the target electrical power Wtrg. Similarly, in the case where the EHC 2 is abnormal (solid curves in FIG. 7), the difference between the actual electrical power Wr12 for the higher initial bed temperature T0 and the target electrical power Wtrg is smaller than the difference between the actual electrical power Wr11 for the lower initial bed temperature T0 and the target electrical power Wtrg. As above, the difference between the actual electrical power Wr and the target electrical power Wtrg is smaller when the initial bed temperature T0 is high than when it is low, whether the EHC 2 is normal or abnormal. In consequence, the difference between the actually supplied electrical energy ΣWr upon the elapse of the specific period of time from the start of the supply of electrical power to the EHC 2 and the target electrical energy Wtrg is smaller when the initial bed temperature T0 is high than when it is low. Therefore, as illustrated in FIG. 8, the value of the supplied electrical energy ratio Prw upon the elapse of the specific period of time from the start of the supply of electrical power to the EHC 2 is larger when the initial bed temperature T0 is high than when it is low, whether the EHC 2 is normal (ΣWr0 represented by the dot-dot-dash curve in FIG. 8) or abnormal (ΣWr1 represented by the solid curve in FIG. 8).

In view of the above, the abnormality detection process according to the embodiment is configured to set the value of the specific ratio Pthre according to the initial bed temperature T0 (or vary the specific ratio Pthre depending on the initial bed temperature T0). Specifically, the value of the specific ratio Pthre is set larger when the initial bed temperature T0 is high than when it is low, as illustrated by the dot-dash curve in FIG. 8. Abnormalities of the EHC 2 can be detected with high accuracy by comparing the supplied electrical energy ratio Prw upon the elapse of the specific period of time from the start of the supply of electrical power to the EHC 2 with the specific ratio Pthre set as above, irrespective of the initial bed temperature T0 even in the case where the catalyst carrier 3 has NTC characteristics.

(Process of Abnormality Detection)

In the following, a process of abnormality detection according to the embodiment will be described with reference to FIG. 9. FIG. 9 is a flow chart of a processing routine executed by the ECU 20 in the abnormality detection according to the embodiment. The processing routine according to the flow chart of FIG. 9 is executed by the ECU 20 and triggered by the start of the above-described preheat process. This processing routine is stored in a ROM or the like of the ECU 20 in advance.

Firstly in step S101 of the processing routine according to the flow chart of FIG. 7, the ECU 20 determines whether or not the preheat process has been started. If a negative determination is made in step S101, the ECU 20 terminates the execution of this processing routine. If an affirmative determination is made in step S101, the ECU 20 proceeds to the processing of step S102.

In step S102, the ECU 20 acquires the initial bed temperature T0 determined in the preheat process and the target electrical power Wtrg set in the preheat process. The initial bed temperature T0 is estimated based on the bed temperature Tend at the time when the operation of the internal combustion engine 1 was stopped last time and the soak time, as described previously with reference to FIG. 3. The target electrical power Wtrg is a constant value that is set taking account of the structure and performance of the devices used to supply electrical power to the EHC 2, as described previously.

In step S103, the ECU 20 calculates the target electrical energy ΣWtrg. Specifically, the ECU 20 calculates the target electrical energy ΣWtrg by adding the target electrical power Wtrg acquired by the processing of step S102 to the previous value ΣWtrgold of the target electrical energy (ΣWtrg=ΣWtrgold+Wtrg). The target electrical energy ΣWtrg is the integrated value of the target electrical power over the period from the start of the supply of electrical power to the EHC 2 to the present time.

In step S104, the ECU 20 acquires the voltage Vehc applied to the electrodes 7 of the EHC 2 (applied voltage) in the preheat process. Then, the ECU 20 proceeds to step S105, where the ECU 20 measures the current (catalyst current) Iehc flowing between the electrodes 7 of the EHC 2 per unit time when the aforementioned applied voltage Vehc is applied to the electrodes 7 by the power supply control unit 18. In step S106, the ECU 20 calculates the electrical power Wr actually supplied to the EHC 2 (actual electrical power) as the product of the applied voltage Vehc acquired by the processing of step S104 and the catalyst current Iehc measured by the process of step S105 (Wr=Vehc*Iehc).

In step S107, the ECU 20 calculates the actually supplied electrical energy ΣWr. Specifically, the ECU 20 adds the electrical power Wr calculated by the processing of step S106 to the previous value ΣWrold of the actually supplied electrical energy to calculate the actually supplied electrical energy ΣWr, which is the integrated value of the actual electrical power over the period from the start of the supply of electrical power to the EHC 2 to the present time.

In step S108, the ECU 20 determines whether or not the target electrical energy ΣWtrg calculated by the processing of step S103 has reached the standard amount of electrical energy ΣWbase. In other words, in step S108, the ECU 20 determines whether or not the specific period has elapsed since the start of the supply of electrical power to the EHC 2. As described previously, the standard amount of electrical energy ΣWbase is the electrical energy that is required to be supplied to the EHC 2 in order to raise the bed temperature Tcat of the catalyst carrier 3 from the initial bed temperature T0 to the specific temperature Ttrg. The lower the initial bed temperature T0 is, the larger the standard amount of electrical energy ΣWbase is. If a negative determination is made in step S108 (ΣWtrg<ΣWbase), the specific period has not been elapsed since the start of the supply of electrical power to the EHC 2 yet. Then, the ECU 20 returns to step S103. If an affirmative determination is made in step S108 (ΣWtrg≥ΣWbase), the specific period has been elapsed since the start of the supply of electrical power to the EHC 2. Then, the ECU 20 proceeds to step S109.

In step S109, the ECU 20 calculates the supplied electrical energy ratio Prw by dividing the actually supplied electrical energy ΣWr calculated by the processing of step S107 by the target electrical energy ΣWtrg calculated by the processing of step S103.

In step S110, the ECU 20 sets the specific ratio Pthre based on the initial bed temperature T0 acquired by the processing of step S102. Specifically, as described previously with reference to FIG. 8, the ECU 20 sets the specific ratio Pthre higher when the initial bed temperature T0 is high than when it is low. For this purpose, relationship between the initial bed temperature T0 and the specific ratio Pthre like that illustrated in FIG. 8 may be stored in the ROM or other component of the ECU 20 in the form of a map or function expression. This enables the ECU 20 to calculate the specific ratio Pthre by accessing the map or function expression using the initial bed temperature T0 acquired by the processing of step S102 as an argument.

In step S111, the ECU 20 determines whether or not the supplied electrical energy ratio Prw calculated by the processing of step S109 is smaller than the specific ratio Pthre set by the processing of step S110. If an affirmative determination is made in step S111 (Prw<Pthre), the ECU 20 proceeds to the processing of step S112, where the ECU 20 determines that the EHC 2 is abnormal. If a negative determination is made in step S111 (Prw≥Prthre), the ECU 20 proceeds to the processing of step S113, where the ECU 20 determines that the EHC 2 is normal.

In the abnormality detection process for the EHC 2 performed according to the flow chart of FIG. 9, the specific ratio Pthre is set according to the initial bed temperature T0. Therefore, this process can detect an abnormality of the EHC 2 with high accuracy irrespective of the initial bed temperature T0, even in the case where the catalyst carrier 3 of the EHC 2 has NTC characteristics.

In this embodiment, the period from the start of supply of electrical power to the EHC 2 to the time when the target electrical energy reaches the standard amount of electrical energy serves as an example of the specific period according to the present disclosure. However, the specific period is not limited to this. The specific period may be any period during which there is a significant difference between the supplied electrical energy ratio with the EHC 2 in a normal condition and that with the EHC 2 in an abnormal condition. For example, the specific period may be the period from the start of supply of electrical power to the EHC 2 to the time when the actual electrical power substantially reaches the target electrical power in the case where the EHC 2 is normal.

In this embodiment, the specific ratio serving as the specific threshold is set based on the initial bed temperature, namely the temperature of the EHC 2 at the time when the supply of electrical power is started. Alternatively, the specific ratio may be set based on the temperature of the EHC 2 at a specific time during the specific period. An example of the specific time is the time at which the actually supplied electrical energy from the time of the start of power supply reaches a predetermined amount of electrical energy. Since the amount of rise in the bed temperature of the catalyst carrier 3 resulting from the supply of the predetermined amount of electrical energy is substantially constant, the bed temperature of the catalyst carrier 3 at the specific time relates to the initial bed temperature. Therefore, the specific ratio is to be set higher when the bed temperature of the catalyst carrier 3 at the specific time is high than when it is low. The bed temperature of the catalyst carrier 3 at the specific time may be either measured by a temperature sensor provided additionally or estimated by adding the amount of rise in the bed temperature resulting from the supply of predetermined amount of electrical energy to the initial bed temperature.

<Modification>

In the above embodiment, detection of an abnormality of the EHC 2 is performed by comparing the supplied electrical energy ratio Prw at the time when the target electrical energy ΣWtrg reaches the standard amount of electrical energy ΣWbase (or at the time when the predetermined time has elapsed since the start of power supply to the EHC 2) with the specific ratio Pthre. Alternatively, detection of an abnormality of the EHC 2 may be performed by comparing the difference between the target electrical energy ΣWtrg and the actually supplied electrical energy ΣWr at the time when the specific period has elapsed since the start of power supply to the EHC 2 (which will also be referred to as the “supplied electrical energy difference”) with a specific difference as the specific threshold. The reason for this is that the difference between the target electrical energy ΣWtrg and the actually supplied electrical energy ΣWr is larger when the EHC 2 is abnormal than when it is normal, and accordingly the supplied electrical energy difference at the time when the predetermined time has elapsed since the start of power supply to the EHC 2 is also larger when the EHC 2 is abnormal than when the it is normal. The supplied electrical energy difference is smaller when the initial bed temperature T0 is high than when it is low, whether the EHC 2 is normal or abnormal. Therefore, the value of the specific difference is to be set smaller when the initial bed temperature T0 is high than when it is low. Detection of abnormality of the EHC 2 performed by comparing the supplied electrical energy difference and the specific difference as above can also enjoy the advantages same as the above-described embodiment. 

What is claimed is:
 1. An abnormality detection apparatus for an electrically heated catalyst comprising: the electrically heated catalyst provided in an exhaust passage of an internal combustion engine, including an exhaust gas purification catalyst and a heating element that generates heat when supplied with electrical power, an electrical resistance of the heating element being larger when a temperature of the heating element is low than when the temperature of the heating element is high; and a controller including at least one processor, the controller configured to: adjust an applied voltage defined as a voltage applied to the electrically heated catalyst in such a way as to make the electrical power equal to a product of the applied voltage and a catalyst current defined as an electrical current flowing through the electrically heated catalyst per unit time equal to a target electrical power to be supplied to the electrically heated catalyst, and adjust the applied voltage to a voltage substantially equal to a specific upper limit voltage when the target electrical power is greater than the specific upper limit voltage and the electrical power supplied to the electrically heated catalyst is lower than or equal to the specific upper limit voltage; calculate an actually supplied electrical energy defined as an integrated value of the electrical power actually supplied to the electrically heated catalyst over a specific period from the time when an application of the applied voltage to the electrically heated catalyst by the controller is started; calculate a target electrical energy defined as an integrated value of the target electrical power over the specific period; calculate an accomplishment ratio parameter equivalent to a ratio of the actually supplied electrical energy calculated by the controller to the target electrical energy calculated by the controller; detect an abnormality of the electrically heated catalyst by comparing the accomplishment ratio parameter calculated by the controller and a specific threshold; acquire a temperature parameter relating to the temperature of the electrically heated catalyst at a time when the supply of electrical power is started; and set the specific threshold according to the temperature parameter acquired by the controller.
 2. The abnormality detection apparatus for an electrically heated catalyst according to claim 1, wherein the controller calculates a supplied electrical energy ratio defined as a ratio of the actually supplied electrical energy calculated by the controller to the target electrical energy calculated by the controller as the accomplishment ratio parameter, the controller determines that the electrically heated catalyst is abnormal if the supplied electrical energy ratio calculated by the controller is lower than a specific ratio as the specific threshold, and the controller sets the specific ratio larger when the temperature parameter acquired by the controller is large than when the temperature parameter acquired by the controller is small.
 3. The abnormality detection apparatus for an electrically heated catalyst according to claim 1, wherein the specific period is a period from a time when the application of the applied voltage to the electrically heated catalyst by the controller is started to a time when the target electrical energy reaches a standard amount of electrical energy.
 4. The abnormality detection apparatus for an electrically heated catalyst according to claim 2, wherein the specific period is a period from a time when the application of the applied voltage to the electrically heated catalyst by the controller is started to a time when the target electrical energy reaches a standard amount of electrical energy. 